The pair had been working on a utility leg of the Brent Bravo rig near where the gas escaped yesterday afternoon.

Sixty non-essential workers were evacuated by coastguard helicopter after the gas was detected on the installation 116 miles north east of Shetland just before 4pm.

A statement from the company said: "Due to the build-up of gas in the utility leg, the platform was downmanned of all non-essential personnel to the nearby Brent Alpha and Brent Charlie platforms. The gas was quickly and safely evacuated."

Police said today that there did not appear to be any suspicious circumstances.

Speaking at a press conference in Aberdeen, Shell Expro Managing Director Tom Botts said: "We are deeply saddened by the deaths of two of our colleagues.

"Our thoughts and prayers are with their families and friends and we will do all that we can to ensure that they are supported through this difficult time.

"We are working closely with the police and the Health and Safety Executive and we are absolutely determined to find out quickly the cause of this incident."

Mr Botts said Shell did not believe the deaths were caused by a so-called kickback, or pocket of gas building up within an oil well.

"That had nothing to do with this particular incident, the men were doing a routine inspection of the utility leg when there was a gas leak in the leg," he said.